Exhaust gas temperature reduction device for aftertreatment devices

ABSTRACT

A motor vehicle exhaust system has at least a first housing for a pollution control element, a nozzle in the housing and a ventilation path into the housing through which outside air is drawn into the exhaust system for mixing with an exhaust flow following the nozzle.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to exhaust systems and more particularly to the reduction of exhaust gas temperature without affecting operation of pollution control elements of the exhaust system.

2. Description of the Problem

Elevated exhaust gas temperatures from the tail pipes of diesel engine equipped motor vehicles have become a greater problem with the introduction of diesel particulate trap/filters (DPF) and the need to regenerate these filters. Diesel particulate filters remove unburned and partially burned hydrocarbons from the exhaust streams produced by diesel engines. A DPF may be periodically regenerated by raising the temperature in the filter sufficiently to accelerate the oxidation of or ignite the particulate matter trapped in the filter. This process, once initiated, further increases the temperature of the exhaust stream downstream from the filter. The increase in the temperature of the exhaust may singe passers by, particularly where the exhaust is discharged near ground level and increase stress on exhaust pipes.

Exhaust system cooling using drawn cooling air is known from U.S. Pat. No. 4,265,332 among other references. In the '332 patent a short extension of exhaust pipe from a muffler is constricted using a venturi. A sleeve (cylindrical heat shield) with an open upstream end is positioned around a portion of an exhaust pipe including the muffler. The sleeve extends past the venturi to become, in effect, an extension of the exhaust pipe. The venturi accelerates the exhaust which in turn draws cooling air through the sleeve and around the exhaust pipe and muffler to a point downstream of the venturi nozzle, where it mixes with the exhaust stream. This cools exhaust system, particularly the muffler, and the air is mixed with the exhaust before final discharge to atmosphere further cooling the exhaust.

U.S. Pat. No. 2,293,632 teaches a cylindrical casing secured around an exhaust pipe. The casing is essentially a elongated tube closed at one end, with a draw tube passing through the closed end. The tube is connected to the exhaust pipe allowing exhaust gas to enter the tube around the draw tube which passes from end to end of the tube. A mixing area is provided at the end of the tube opposite the closed end and mixed exhaust/outside air pass from the tube through the tube end opposite the closed end. No particular relationship between the casing and and components in the exhaust system, such as a muffler, is discussed. Given the reference was filed in the early 1940's it is not believed that consequences for pollution control features of the exhaust system were considered.

U.S. Pat. No. 3,186,511 teaches an air jet exhaust muffler in which air inlets introduce outside air to an exhaust stack both at the forward end of the muffler and into the exhaust pipe following the muffler.

The prior art frequently, though not universally, achieved exhaust gas cooling as a byproduct of cooling a component, such as a muffler, in the exhaust system. In some contemporary pollution control schemes components of the exhaust gas treatment system must run hot in order to operate or regenerate making it undesirable to reduce exhaust gas temperature ahead of the component in question or to reduce the temperature of the component itself. For example, diesel particulate trap/filter regeneration however requires maintaining the temperature of the trap during regeneration. However, there remains a need to cool the exhaust gas, but only after the exhaust leaves the trap/filter. It remains desirable to protect pipes of the exhaust system from the high temperatures which attach to the casing housing the filter and well as reduce the danger of singing passers-by.

SUMMARY OF THE INVENTION

The invention provides for cooling of the exhaust flow from a motor vehicle exhaust system before discharge into the environment by providing for drawing ambient air into the exhaust stream. The exhaust system includes elements providing air pollution treatment, such as catalytic converters and particulate filters for diesel vehicles. The catalytic converters and diesel particulate filters are installed in canisters or housings replacing portions of the exhaust pipe in the exhaust system. While either element can be a heat source, diesel particulate filters are subject to particularly high temperatures, which are required for regeneration of the filter. Passive cooling of the exhaust through ventilation of the exhaust system is provided by drawing outside air into a casing of the exhaust stream without significant reduction of the operating temperature of the pollution treatment element, particularly in the case of diesel particulate filters. Cooling is advantageously introduced to the exhaust system through the housing just aft of the element to reduce the temperature of the exhaust gas as it is returned to the exhaust pipe proper without affecting operation of the pollution control element.

A ventilation path into the housing which allows air to be drawn into the exhaust system is defined within a flow diverting element positioned in the housing. The flow diverting element is preferably a streamlined bulb having an open downstream end. The bulb is positioned centered in the flow channel defined by the housing, in effect forming a converging/diverging nozzle within the housing. The bulb is positioned by mounting wings extending from the bulb to the walls of the housing. The bulb and the wings are hollow and the interior sections of the wings are coupled to the outside air through the walls of the housing. The bulb operates as a venturi in the channel increasing the velocity of the flow and producing a partial vacuum relative to ambient pressure in the stream adjacent the downstream outlet from the bulb. The bulb also introduces turbulence into the flow. The partial vacuum draws air through the wings and bulb out the downstream open end from the bulb where turbulence promotes quick mixing of the air with the exhaust before discharge into an exhaust pipe.

Additional effects, features and advantages will be apparent in the written description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a school bus which may be equipped with an exhaust system modified to incorporate the present invention.

FIG. 2 is a plan form view of a diesel engine exhaust system.

FIG. 3 is a perspective view of a diesel particulate filter canister modified to incorporate the present invention.

FIG. 4 is a perspective view in partial phantom illustrating a flow constriction bulb has taught by the present invention.

FIG. 5 is a cross sectional view of a portion of a diesel particulate filter canister incorporating the invention.

FIG. 6 is a cross section view of a portion of a diesel particulate filter canister incorporating the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings and in particular referring to FIG. 1 a vehicle such as a school bus 100, which is typically equipped with a diesel engine requiring use of a diesel particulate filter (DPF), is shown. In a vehicle such as school bus 100 the tail pipe 112 of an exhaust system typically runs under the vehicle to a point of discharge 114 along the side or back of the vehicle. The point of discharge 114 is at a level where passers-by can be directly exposed to discharge of exhaust from the pipe 112.

FIG. 2 illustrates an exhaust treatment system 15 for a vehicle 11 with a catalytic converter 18 and a diesel particulate filter housing 22 connected in series to treat exhaust generated by operation of engine 12. The exhaust system 15 is shown installed on the motor vehicle 11, and it may be positioned in any attitude, such as vertically or horizontally or under the cab. The engine 12 is in fluid communication with the exhaust treatment system 15 through tubing 14 extending from an exhaust manifold (not shown) to the inlet side of the catalytic converter 18. The exhaust gas is transported from an outlet end of the catalytic converter 18 by a pipe 24 to the inlet end of a diesel particulate filter housing 22. Treated exhaust flow from the diesel particulate filter housing passes through outlet tubing 40 (shown in FIG. 3) to an exhaust pipe 16, which can include a tailpipe extension or stack 34, though in its preferred embodiment the invention is more advantageously applied to a tailpipe extension than to a vertical stack.

The diesel particulate filter housing 22 encloses a diesel particulate filter 20 in its forward portion. An inlet 38 from the outside air into the interior of housing 22 downstream from the filter 20 is provided. As is known in the art, diesel particulate filter 20 is subject to periodic regeneration which involves an increase in the operating temperature within the housing on the order of hundreds of degrees Celsius. Exhaust gas ejected from a tailpipe can be expected to exhibit substantial increases in temperature as a result. There exists a need to reduce the temperature of the exhaust gas without reducing the temperature of the portion of housing 22 in which the filter 20 is located.

Referring now to FIG. 3, the exterior of a digital particulate filter housing 22 modified in accordance with the teachings of the present invention is illustrated. One of two inlets 38 into the housing/canister 22 is visible on the cylindrical shell 23 of the housing 22. An outlet tube 40 provides for connection to an exhaust pipe. Tube 40 preferably fits within an exhaust pipe and is made of materials with greater temperature resistance than the exhaust pipe.

Referring to FIG. 4, flow through a channel 41 defined with housing 20 (shown in phantom) as well as exterior details of a flow directing bulb 42 positioned in the channel are illustrated. Bulb 42 is streamlined in the direction facing the flow of exhaust (indicated by the broad arrow marked “flow”) and has an open end 49 centered on the flow axis downstream. The downstream end of bulb 42 protrudes slightly into a base end of outlet tube 40 to produce an area of maximum flow constriction substantially adjacent and surrounding open end 49. Bulb 42 is suspended within flow channel 41 by a pair of mounting wings/struts 44 which extend outwardly from the bulb and attach to the cylindrical wall 23. Mounting wings/struts 44 have hollow interiors 47 leading from outside of housing 23 to the interior of bulb 42. Alternative shapes for the fresh air conduit are of course possible and in some configurations it is not necessary that the fresh air paths join before the outlet from the fresh air conduit. The points are that the conduit is streamlined, is positioned in the air flow channel of the housing in a way so as to constrict and effect acceleration of the exhaust flow and that ambient air is piped into the housing for mixture with the exhaust in a way that does not cool the pollution control element.

Referring to FIG. 5, a ventilation path 50 through the wing mounts 42 into the interior 51 of bulb 42 and out of outlet port 49 into outlet pipe 40 is shown. Bulb 42 is a flow diverting element which converts the downstream end of housing 23 into a nozzle which is most constricted across a ring surrounding the orifice/outlet port 49. (The ring surrounding bulb 42 might be more fairly described as a pair of ring arcs since the wing mounts interrupt the full ring.) Ambient air drawn along the ventilation path 50 mixes with exhaust gases within outlet pipe 40 before passing to a tail pipe 16, which is typically constructed from materials not having the capacity to withstand heat that housing 20 is constructed from. Bulb 50 is streamlined and closed where it faces the incoming exhaust stream and enclosed everywhere up to the ring of maximum constriction. Bulb 42 has an open downstream end. The bulb 42 is positioned centered in the flow channel defined by the housing and in effect forms a converging/diverging nozzle within the housing 23. The bulb 42 operates as a venturi in the channel increasing the velocity of the flow and producing a partial vacuum relative to ambient pressure in the stream adjacent the downstream outlet from the bulb. The bulb 42 also introduces turbulence into the exhaust flow. The partial vacuum draws air through the wings and bulb out a downstream open end 49 from the bulb 42 where turbulence promotes quick mixing of the air with the exhaust before discharge into an exhaust pipe.

Referring to FIG. 6 and alternative cross sectional view of bulb 50 is shown, with housing 23 rotated ninety degrees on its long axis.

While the invention is shown in only two of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention. 

1. Apparatus comprising: a housing having an inlet, an outlet and defining a channel for a fluid from the inlet to the outlet; a bulb having a hollow interior with the bulb located in the channel and having a closed end defining an upstream end of the bulb in the channel and an open end defining a downstream end of the bulb, the bulb being disposed in the channel to constrict the flow of a fluid in the channel; at least a first opening through the housing; and the bulb being mounted from the housing by at least a first wing conduit, said at least first wing conduit being connected between said first opening and hollow interior of the bulb.
 2. Apparatus as claimed in claim 1, further comprising: a second wing opening in the housing; and a second wing conduit connecting the bulb to the housing, the second wing conduit being hollow and providing fluid communication between the hollow interior of the bulb and outside of the housing through the second opening.
 3. Apparatus as claimed in claim 2, further comprising: the bulb being located in the channel to position its open end to discharge into the outlet and to not occupy a substantial portion of the channel upstream from the bulb.
 4. An exhaust system for a motor vehicle engine comprising: a treatment system for a vehicle exhaust stream including a plurality of housings disposed along an exhaust pipe, the exhaust pipe and housings defining a conduit; and a ventilation path for drawing ambient air into the vehicle exhaust stream at a point of discharge from at least a first housing to cool the vehicle exhaust, the ventilation path including a bulb mounted within said at least first housing to constrict the conduit within the housing, the bulb having a hollow interior, mounts between the bulb and the housing to fix the position of the bulb, channels through the mounts fluidically connecting the hollow interior to outside of the housing, the bulb having an open downstream end to allow fluid communication between the hollow interior and the conduit.
 5. An exhaust system for a motor vehicle in accordance with claim 4, further comprising: the open downstream end of the bulb being located to discharge into the exhaust pipe.
 6. An exhaust system for a motor vehicle in accordance with claim 5, the bulb being generally rounded and enclosed at an upstream end.
 7. An exhaust system for a motor vehicle in accordance with claim 6, the housing containing a diesel particulate filter subject to high temperature regeneration.
 8. An exhaust system for a motor vehicle in accordance with claim 7, the bulb and interior of the housing defining a venturi for promoting mixing of an exhaust stream with outside air drawn through the bulb downstream from the venturi.
 9. A motor vehicle comprises an exhaust system having at least a first housing for a pollution control element, a nozzle in the housing and a conduit defining a ventilation path into the housing through which outside air is drawn into the exhaust system for mixing with an exhaust flow, the conduit having an orifice discharge from the ventilation path into the exhaust system after the nozzle.
 10. A motor vehicle in accordance with claim 9, wherein the nozzle is formed in ring arcs between the housing and the conduit. 